Biodiesel, one of the renewable energy sources, is made from vegetable oils, animal fats or waste oils, such as cooking oils, as shown in FIG. 1.
Biodiesel has been widely used in many countries and regions, such as US, Europe and Japan, as a clean renewable energy. Up to now, biodiesel has not been industrialized in China. The methods for biodiesel production mainly include:
(1) chemical method, which is mainly used in industry at present, wherein the glycerol-group of vegetable oils or animal oils is substituted by low-carbon alcohols such as methanol or ethanol to produce corresponding fatty acid methyl esters or fatty acid ethyl esters by transesterification in the presence of acidic or basic catalysts (Ma F, Hanna M A. Biodiesel production: a review. Bioresource Technology, 1999, 70: 1˜15).
(2) biological method, wherein biological enzymes or cells are used to catalyze transesterification reaction and the corresponding fatty acid methyl esters or fatty acid ethyl esters are produced (Ma F, Hanna M A. Biodiesel production: a review. Bioresource Technology, 1999, 70: 1˜15).
(3) supercritical method, wherein transesterification reaction is carried out in a supercritical solvent system without any catalysts. (Saka S, Kusdiana D. Biodiesel fuel from rapeseed oil as prepared in supercritical methanol. Fuel, 2001, 80 (2): 225˜231; Kusdiana D, Saka S. Kinetics of transesterification in rapeseed oil to biodiesel fuel as treated in supercritical methanol. Fuel, 2001, 80 (5): 693˜698; Miao Xiao-ling, Wu Qing-yu, Exploitation of biomass renewable energy sources of microalgae. Renewable Energy, 2003, No. 3: 13˜16).
During the production of biodiesel using above methods, a by-product, glycerol, is obtained. With the biodiesel production increasingly growing up, the glycerol production is increased correspondingly. How to efficiently utilize the glycerol, a by-product from biodiesel production, becomes a common problem for large amount of biodiesel production.
As an organic solvent, 1,3-propanediol (PDO) is an important chemical raw material in industries, such as in the areas of printing ink, dying, coating, lubricant, and anti-freeze agent. 1,3-propanediol is mainly used as monomer in the synthesis of polyesters and polyurethanes, especially in the synthesis of poly(trimethylene terephthalate) (PTT) by polymerization of terephthalic acid and 1,3-propanediol, exhibiting an advantageous characteristic over the traditional polymers obtained by the polymerization of monomer 1,2-propanediol, butanediol, or ethanediol. Tens of million tons of poly(ethylene terephthalate) (PET) are consumed all over the world yearly. PTT has comparable chemical stability and biological degradability with those of PET, but is more advantageous in terms of pollution resistance, ductility and elastic resilience as well as ultraviolet resistance. In addition, PTT fibers have the advantages of wear-resistance, low water absorbability and weak static, and are able to compete with nylon in carpet industry. It also can be used in non-woven fabrics, engineering plastics, clothing, household ornaments, paddings and fabrics. PTT was evaluated as one of 1998's Six New Petrochemical Products in the US and considered as an alternative of PET.
The superior performance and commercial potential of PTT has been recognized as early as 50 years ago. It is very difficult to produce PTT in an industrial scale due to the difficulty and high cost of 1,3-propanediol production. Currently, only DuPont and Shell can synthesize 1,3-propanediol for the production of PTT in large scale, employing oxane or propene as raw materials. The disadvantages of chemical method include, for example, more by-products, poor selectivity, high temperature and pressure required for operation, excessive investment in equipment, non-renewable raw material, and inflammable, explosive or extremely toxicity of oxane and acrolein, an intermediate of another synthesis pathway. The production of 1,3-propanediol by fermentation has become the focus of attention in recent years because of its high selectivity and mild operation conditions. Now, the main routes of the production of 1,3-propanediol from glycerol by fermentation include:
1) conversion of glycerol to 1,3-propanediol by fermentation under anaerobic condition using Enterobacteria (U.S. Pat. No. 5,254,467, EP0373230 A1).
2) production of 1,3-propanediol by fermentation under anaerobic condition using anaerobic bacteria such as Klebsiella (Ruch et al. Regulation of glycerol catabolism in Klebsiella aerogenes. J. Bacteriol. 1974, 119(1):50˜56; Streekstra et al. Overflow metabolism during anaeric growth of Klebsiella pneumoniae NCTC418 on glycerol and dihydroxyacetone in chemostat culture. Arch Microbiol. 1987, 147:268˜275; Zeng et al. Pathway analysis of glycerol fermentation by Klebsiella pneumoniae: Regulation of reducing equivalent balance and product formation. Enzyme Microbiol Technol. 1993, 15:770˜779).
3) production of 1,3-propanediol by fermentation under microaerobic condition using Klebsiella (Wang Jian-feng et al, Study on microaerobic conversion of glycerol to 1,3-propanediol by Klebsielle pneumoniae. Modern Chemical Industry, 2001, 21 (5): 28-31. Xiu Zhi-long et al, A method of production of 1,3-propanediol by fermentation using microbes under microaerobic condition, Chinese Patent Publication No.: CN1348007).
4) production of 1,3-propanediol and 2,3-butanediol by fermentation under anaerobic condition using Klebsiella (Biebl et al. Fermentation of glycerol to 1,3-propanediol and 2,3-butanediol. Appl Microbiol Biotechnol, 1998, 50:24-29).
The raw materials used in above routes are all from the reagent glycerol or the fermentation broth containing glycerol. Up to now, there is no report on the production of 1,3-propanediol by fermentation of crude glycerol, a by-product from biodiesel production. Xiu Zhi-long et al (Xiu Zhi-long et al, A linked method of production of biodiesel and 1,3-propanediol, Chinese Patent Publication No.: CN1648207A) proposed that glycerol could be isolated by filtering the by-products from biodiesel production through membrane and used to produce 1,3-propanediol by fermentation, but this method is hard to carry out due to the cost of membrane filter and the difficulties of cleaning and regenerating the membranes. Moreover it is very difficult to perform both processes simultaneously, especially production in a large scale.